I would like to get the best teacher training to become a fully qualified TEFL teacher. I'm interested in distance learning and more particularly in DELTA. Do you think I need another teacher qualification to book for this course ?

I suppose you cannot have DELTA without having CELTA first, it is something similar to applying for Masters without doing Bachelor first. Also, I am not a big fan of online courses. Face-to-face interaction works better, I say.

You do not need to hold a CELTA to register in a DELTA course. All is required in terms of prior qualifications is a degree or an initial teaching qualification. See their official website for details.